Sub-picosecond electro-optic measurement of relativistic electron pulses

Time-resolved measurements of the transverse electric field associated with relativistic electron bunches are presented. Using an ultra-fast electro-optic sensor close to the electron beam, the longitudinal profile of the electric field could be measured with sub-picosecond time resolution and without time-reversal abiguity. Results are shown for two cases: inside the vacuum beam line in the presence of wake fields, and in air behind a Be window, effectively probing the near-field transition radiation. Especially in the later case, reconstruction of the longitudinal electron bunch shape is straightforward.